Use of echinacea to reduce irritation and boost anti-aging efficacy of cosmetic compositions containing hydroxy acids.
Some ingredients used in topical products are potentially irritating, especially to people with xe2x80x9csensitive skin.xe2x80x9d
As an example, hydroxy acids (HAs) have been proven to deliver cosmetic benefits, such as improvement in the appearance of photodamaged or naturally aged skin, skin lightening, treatment of age spots, etc. Unfortunately, their use at high concentrations may occasionally be associated with skin irritation, e.g. skin redness and stinging sensation upon application. The irritation can be ameliorated by lowering the amount of an active ingredient in the composition or by reducing the active""s penetration through the skin. A serious drawback of both approaches is that the efficacy is impaired. The HA related irritation can be reduced by raising the composition""s pH but this method yields reduced efficacy due to a decreased HA penetration through the skin. It is desirable to reduce or eliminate the irritation potential of HAs while maintaining their efficacy.
The need exists, therefore, for a composition and method that prevents or reduces the skin irritation which may be caused by hydroxy acids.
U.S. Pat. No. 5,705,170 (Kong et al.) discloses an herbal cellulite treatment and a cosmetic composition which may contain from 0.1 to 20% wt. of an alpha hydroxy acid. The composition has a pH of from 3-6; echinacea extract is used in the example at a level of 2%. U.S. Pat. No. 5,667,791 (Hersh et al.) discloses a topical composition which may be in the form of a lotion, cream, oil or gel. One of the exemplified compositions contains 0.047% of echinacea and 0.018% of lactic acid. The compositions are used to reduce and repair X-ray radiation induced skin damage. U.S. Pat. No. 5,804,168 (Murad) discloses a composition which may be in the form of cream, paste, gel or ointment or emulsion and may be applied topically for treatment of sun-damaged skin. The composition may contain echinacea and lactic acid. The latter is used in the example at the level of 5.6% wt.
The present invention provides a method for reducing skin irritation caused by the topical application of a composition containing HAs, the method comprising topically applying echinacea extract. Echinacea extract may be co-present with HAs in the same composition, or may be applied from a separate composition.
According to the present invention, by virtue of topical application of echinacea extract, the skin irritation caused by HAs is reduced or eliminated.
Furthermore, it has been found according to the present invention that echinacea has an additional valuable effect of significantly boosting the anti-aging efficacy of HAs. Thus, when echinacea extract is present in the composition, HAs can be used in a lower amount, without reduction in efficacy, and thus reducing skin irritation potential even further.
The present invention also includes a cosmetic skin care composition containing HAs and Echinacea purpurea or Echinacea pallida. 
Except in the operating and comparative examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts of material or conditions of reaction, physical properties of materials and/or use are to be understood as modified by the word xe2x80x9cabout.xe2x80x9d All amounts are by weight of the composition, unless otherwise specified.
Echinacea extract is employed in the inventive compositions to reduce or eliminate the skin irritation caused by HAs and/or to boost anti-aging effect of HAs. Echinacea extract, also known as Coneflower extract, can be purchased from commercial suppliers such as BioBotanica. Echinacea extract is used in the inventive compositions and methods in a concentration of from 0.1 to 20%; preferably from 0.5 to 10%, most preferably from 0.5 to 5%.
Echinacea extract may be obtained from the following echinacea species: Echinacea angustifolia, Echinacea purpurea, Echinacea pallida. Echinacea purpurea is preferred according to the present invention since it contains chicoric acid, which was shown, as part of the present invention to have anti-irritant activity. Echinacea purpurea is also commercially available. Echinacea pallida also contains chocoric acid, but it is not commercially available.
The hydroxy acid can be chosen from alpha-hydroxy acids, beta-hydroxyacids (e.g. salicylic acid), other hydroxycarboxylic acids (e.g., dihydroxycarboxylic acid, hydroxy-dicarboxylic, hydroxytricarboxylic) and mixtures thereof or combination of their stereoisomers (DL, D or L).
Preferably the hydroxy acid is chosen from alpha-hydroxy acids having the general structure (1) 
where M is H or a saturated or an unsaturated, straight or branched hydrocarbon chain containing from 1 to 27 carbon atoms.
Even more preferably the hydroxy acid is chosen from lactic acid, 2-hydroxyoctanoic acid, hydroxylauric acid, glycolic acid, and mixtures thereof. When stereo isomers exist, L-isomer is most preferred.
It is to be understood that depending on the pH of the composition, the hydroxy acid may be present as a salt, e.g. ammonium or potassium or sodium salt.
Although echinacea extract may be included into compositions that have any pH in the general range of 2.5 to 10, the inventive methods are particularly useful when compositions are at an acidic pH (especially if they contain a hydroxy acid), preferably 3-5 and most preferably at a pH of 3-4, because such compositions are particularly irritating.
A particular advantage of the inventive methods is that higher amounts of hydroxy acids may be employed without causing skin irritation. Preferably the amount of the hydroxy acid component present in the composition is from 0.01 to 20%, more preferably from 2 to 12% and most preferably from 4 to 12% by weight.
Glycolic acid and/or lactic acid are most preferred because although these ingredients have been found to cause irritation, they were found to be particularly efficacious at delivering cosmetic benefits.
The compositions and methods according to the invention also comprise a cosmetically acceptable vehicle to act as a diluent, dispersant or carrier for the active ingredients in the composition, so as to facilitate their distribution when the composition is applied to the skin.
Vehicles other than water can include liquid or solid emollients, solvents, humectants, thickeners and powders. An especially preferred nonaqueous carrier is a polydimethyl siloxane and/or a polydimethyl phenyl siloxane. Silicones of this invention may be those with viscosities ranging anywhere from about 10 to 10,000,000 centistokes at 25xc2x0 C. Especially desirable are mixtures of low and high viscosity silicones. These silicones are available from the General Electric Company under trademarks Vicasil, SE and SF and from the Dow Corning Company under the 200 and 550 Series. Amounts of silicone which can be utilized in the compositions of this invention range anywhere from 5 to 95%, preferably from 25 to 90% by weight of the composition. The amount of vehicle may range from about 2 to about 99 wt %, preferably from about 50 to about 99%, most preferably from about 80 to 99%, by weight of the total composition.
According to the present invention, the vehicle is preferably at least 60 wt. % water, by weight of the vehicle. The inventive compositions are preferably oil-in-water emulsions, in order to improve dermal delivery of hydroxy acids (See Sah A., xe2x80x9cAn in-vitro study of the effect of formulation variables and product structure on the delivery of alpha-hydroxy acid (Lactic acid) to skinxe2x80x9d, MS Thesis, Department of Pharmaceutical Sciences of the College of Pharmacy, University of Cincinnati, Ohio, July 1996). Such improved delivery is frequently accompanied by increased irritation/sting, making the use of echinacea extract in such emulsions particularly critical. In the preferred oil-in-water emulsions according to the present invention, water comprises at least 50 wt. % of the inventive emulsion, most preferably from 50 to 70 wt. %, by weight of the composition.
Optional Skin Benefit Materials and Cosmetic Adjuncts
Various types of active ingredients may be present in cosmetic compositions of the present invention. Actives are defined as skin benefit agents other than emollients and other than ingredients that merely improve the physical characteristics of the composition. Although not limited to this category, general examples include anti-wrinkle compounds and sunscreens and tanning agents.
Sunscreens include those materials commonly employed to block ultraviolet light. Illustrative compounds are titanium dioxide, the derivatives of PABA, cinnamate and salicylate. For example, octyl methoxycinnamate and 2-hydroxy-4-methoxy benzophenone (also known as oxybenzone) can be used. Octyl methoxycinnamate and 2-hydroxy-4-methoxy benzophenone are commercially available under the trademarks, Parsol MCX and Benzophenone-3, respectively. The exact amount of sunscreen employed in the emulsions can vary depending upon the degree of protection desired from the sun""s UV radiation.
Another category of functional ingredients within the cosmetic compositions of the present invention are thickeners. A thickener will usually be present in amounts anywhere from 0.1 to 20% by weight, preferably from about 0.5% to 10% by weight of the composition. Exemplary thickeners are cross-linked polyacrylate materials available under the trademark Carbopol from the B.F. Goodrich Company. Gums may be employed such as xanthan, carrageenan, gelatin, karaya, pectin and locust beans gum. Under certain circumstances the thickening function may be accomplished by a material also serving as a silicone or emollient. For instance, silicone gums in excess of 10 centistokes and esters such as glycerol stearate have dual functionality.
Powders may be incorporated into the cosmetic composition of the invention. These powders include chalk, talc, Fullers earth, kaolin, starch, smectite clays, chemically modified magnesium aluminum silicate, organically modified montmorillonite clay, hydrated aluminum silicate, fumed silica, aluminum starch octenyl succinate and mixtures thereof.
Other adjunct minor components may also be incorporated into the cosmetic compositions. These ingredients may include coloring agents, opacifiers and perfumes. Amounts of these other component materials may range anywhere from 0.001% up to 20% by weight of the composition.
Use of the Composition
The composition according to the invention is intended primarily as a product for topical application to human skin, especially as an agent for conditioning and smoothening the skin, and preventing or reducing the appearance of wrinkled, aged and/or photodamaged skin, or lightening or evening of skin color and tone.
In use, a small quantity of the composition, for example from 1 to 100 ml, is applied to exposed areas of the skin, from a suitable container or applicator and, if necessary, it is then spread over and/or rubbed into the skin using the hand or fingers or a suitable device.